I have a recurring graphics problem. In a battle areas of the ground and sky become boxes of many colors and sometimes large streaks of color will come off units, buildings etc. I received help for this on here once by turning off write combining and it worked for a while but now the problems are back again

System Specs
AMD Sempron Processor 3100+
512 MB RAM
Radeon 9800XT graphics card
After you have finished laughing at my pathetic specs any suggestions would be great...

I have the ATI catalyst center if you're familiar with it.